If it's self hosted, you shouldn't care if it costs money. Let the person/org decide if they want to use it, just provide an interface for it. There are tons of free, self hosted apps that have tons of notification methods available. Radarr alone has 26 methods for notifications, none enabled by default. They include generic webhook, "custom script", and then there a number of specific ones where you put in the URL, API key, etc. and as the person hosting it things would go against my API count/bill. There's no need for you to be specific about Twilio, just have a notification framework with Twilio being one of the providers.